Within power line communication systems there is provided a 3 phase power supply to power a load. If this supply were to power a perfectly balanced load the voltage between the neutral point of the supply and the neutral point of the load would be 0 volts. Subsequently, if both the supply neutral and the load neutral were connected using a neutral wire or both were connected to earth, then the current flow in this neutral or earth link would be 0 amps.
However, electrical systems are not perfectly balanced and for a motor powered over a long cable with various junction boxes and connectors, each phases impedance will be affected by a multitude of factors, such as: the length of the cable, the connection resistance, the position of the winding in the slot, the differences in winding lengths, the construction of the motor, the construction of the cable and the transposition of the cable. Such imbalances in a load create a voltage difference between the two neutral points and as current flow between the two neutrals is undesirable as it will cause a loss of power and they are not typically connected.
Power line communication systems are well known in the art. One such known system provides a means of communicating data from a remote inductive electrical load, such as a motor by modulating the motor current. However this type of system may require the need for modifying the motor windings.
Other existing PLC methods which use earth link currents, use a DC coupled current to act as the communication carrier. This however requires a large coupling package at both the supply and the load neutral connection, which are designed to remove signals above a few Hertz to remove the known imbalance voltage differences and as such limits the data transfer rate to a few bits per second. Furthermore, these types of coupled signals also suffer from the fact that they transfer less power to the transmitter.
It is an object of at least one aspect of the present invention to obviate or mitigate one or more of the aforementioned problems and disadvantages.